Southdown Motor Services was a bus and coach operator in East and West Sussex and parts of Hampshire, in southern England. It was formed in 1915 and had various owners throughout its history, being purchased by the National Bus Company (NBC) in 1969. The company fleet name was lost when it was acquired by the Stagecoach Group in 1989 but buses operated under that legal name until 2015 when the operating licence was transferred to another company within the Stagecoach Group and 1915 company became dormant but still owned by the Stagecoach Group.

A coach is a type of bus built for longer-distance service, in contrast to transit buses that are typically used within a single metropolitan region. Often used for touring, intercity, and international bus service, coaches are also used for private charter for various purposes. Coaches are also related and fall under a specific category/type of RVs.